docs: def _paint_line_number_bg(self, im):
          """
          Paint the line number background on the image.
          """
          if not self.line_numbers:
              return
          if self.line_number_fg is None:
              return
          draw = ImageDraw.Draw(im)
          recth = im.size[-1]
          rectw = self.image_pad + self.line_number_width - self.line_number_pad
          draw.rectangle([(0, 0), (rectw, recth)],
                         fill=self.line_number_bg)
          draw.line([(rectw, 0), (rectw, recth)], fill=self.line_number_fg)
          del draw